Electronic monitoring systems of a similar type have previously been described. In U.S. Pat. No. 4,543,566 an electronic monitoring system comprising a contact less movement detector is described. The movement detector comprises an oscillator with a sensing coil, having an output connected to an input of a first gate with another input connected to a square wave generator, the pulses of which appear at the output of the first gate, with or without phase inversion depending on the output voltage of the movement detector. These pulses are fed, via an amplifier, to an input of a second gate, the input of which directly receives the output pulses from the square wave generator, but having a delay. If a fault occurs, disturbing the pulse transmission to any of the inputs to this second gate, its output becomes a pulsating voltage. Further, an integrator being parallel coupled with the second gate to the amplifier output can introduce such a fault.